1. Field of the Invention
The present invention relates to a detector which extracts a beat position from an audio signal such as a tone signal, for example, obtained on the basis of a musical instrument played by a performer.
The present invention also relates to a synchronization control device which controls the synchronization of a musical instrument control device such as a MIDI (Musical Instrument Digital Interface) sequencer on the basis of the extracted beat position.
2. Description of the Related Art
Conventionally, when a musical instrument control device such as a MIDI sequencer and a recording and reproducing device such as an analog multitrack recorder are synchronized, precise speed control of the recording and reproducing device is impossible. Therefore, it is necessary to record a synchronization signal on a predetermined track of a recording medium in the recording and reproducing device and to provide synchronous control of a musical instrument control device on the basis of a synchronization signal reproduced from the recording and reproducing device.
Recently, a digital multitrack recorder (hereinafter referred to as "DMTR") is marked as a recording and reproducing device which uses a digital recording medium such as a hard disc which records digital data. In the DMTR, an analog audio signal obtained by a performer's performance is converted to digital audio signals at predetermined sample intervals and the digital audio signals are then recorded sequentially at successive addresses on a digital recording medium. Therefore, digital audio signals recorded at the respective addresses on the digital recording medium correspond accurately to a time elapsing from the start of recording using a clock from an oscillator as a reference. By operating the musical instrument control device in accordance with the clock from the DMTR, the musical instrument control device is easily and accurately synchronized with the DMTR.
For example, the DMTR generates an MIDI clock on the basis of a clock from its internal oscillator, and delivers it as an MIDI message to an MIDI sequencer, which provides automatic performance control over an electronic musical instrument or the like in accordance with the MIDI clock. The performer plays his own musical instrument to that automatic performance. An audio signal obtained by the performer's performance is recorded on the DMTR. In reproduction, the DMTR delivers to the MIDI sequencer the same MIDI clock as that in recording while reproducing a recorded audio signal. Thus, the reproduction of the audio signal and automatic performance of the musical instrument by the MIDI sequencer are synchronized accurately.
Some persons want to reproduce an audio signal recorded already in the recording and reproducing device while synchronizing automatic performance of the instrument by the MIDI sequencer with the reproduction. In such a case, the MIDI sequencer is required to be synchronized with the tempo of the reproduced audio signal. The tempo of the audio signal can vary depending on the performance of the instrument by the performer which has caused that audio signal to be generated. Thus, it is required to extract a beat position from the audio signal and to produce an MIDI clock on the basis of the beat position.
A conventional example of extracting a beat position from an audio signal is a system in which the user inputs data on a beat position by a manual operation. In this system, the user beforehand reproduces an audio signal from the recording and reproducing device while tapping predetermined input keys to the tempo of the audio signal. By this operation, information on the reproducing positions of the audio signals reproduced at the respective points of time when the input keys are tapped are recorded sequentially as the beat positions in a memory. In actual synchronous reproduction, the recording and reproducing device reproduces an audio signal while producing an MIDI clock at each of the timings obtained by dividing into a predetermined number of subintervals the interval from a reproduction position where the beat position exists to a reproduction position where the next beat position exists.
However, in the above conventional example, the user is required to listen the audio signal while performing the tapping operation without mistakes from the head of the audio signal to its end, so that he is required to have immense attentiveness and perseverance. He is forced to perform a long-time operation depending on the music. Thus, his fatigue and the probability of failure are high, and this system can not be said to be a practical one.